block: add logical block provisioning info to BlockDriverInfo

Reviewed-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Peter Lieven <pl@kamp.de>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>

include/block/block.h

@@ -18,6 +18,22 @@ typedef struct BlockDriverInfo {
     /* offset at which the VM state can be saved (0 if not possible) */
     int64_t vm_state_offset;
     bool is_dirty;
+    /*
+     * True if unallocated blocks read back as zeroes. This is equivalent
+     * to the the LBPRZ flag in the SCSI logical block provisioning page.
+     */
+    bool unallocated_blocks_are_zero;
+    /*
+     * True if the driver can optimize writing zeroes by unmapping
+     * sectors. This is equivalent to the BLKDISCARDZEROES ioctl in Linux
+     * with the difference that in qemu a discard is allowed to silently
+     * fail. Therefore we have to use bdrv_write_zeroes with the
+     * BDRV_REQ_MAY_UNMAP flag for an optimized zero write with unmapping.
+     * After this call the driver has to guarantee that the contents read
+     * back as zero. It is additionally required that the block device is
+     * opened with BDRV_O_UNMAP flag for this to work.
+     */
+    bool can_write_zeroes_with_unmap;
 } BlockDriverInfo;
 
 typedef struct BlockFragInfo {